How big a deal is the surprise primary defeat of Rep. Eric Cantor, the House majority leader? Very big. Movement conservatism, which dominated American politics from the election of Ronald Reagan to the election of Barack Obama — and which many pundits thought could make a comeback this year — is unraveling before our eyes.

I don’t mean that conservatism in general is dying. But what I and others mean by “movement conservatism,” a term I think I learned from historian Rick Perlstein, is something more specific: an interlocking set of institutions and alliances that won elections by stoking cultural and racial anxiety but used these victories mainly to push an elitist economic agenda, meanwhile providing a support network for political and ideological loyalists.

By rejecting Cantor, the Republican base showed that it has gotten wise to the electoral bait and switch, and, by his fall, Cantor showed that the support network can no longer guarantee job security. For around three decades, the conservative fix was in; but no more.

To see what I mean by bait and switch, think about what happened in 2004. George W. Bush won re-election by posing as a champion of national security and traditional values — as I like to say, he ran as America’s defender against gay-married terrorists — then turned immediately to his real priority: privatizing Social Security.

It was the perfect illustration of the strategy famously described in Thomas Frank’s book “What’s the Matter With Kansas?” in which Republicans would mobilize voters with social issues but invariably turn post-election to serving the interests of corporations and the 1 percent.

In return for this service, businesses and the wealthy provided both lavish financial support for right-minded (in both senses) politicians and a safety net — “wing-nut welfare” — for loyalists. In particular, there were always comfortable berths waiting for those who left office, voluntarily or otherwise. There were lobbying jobs; there were commentator spots at Fox News and elsewhere (two former Bush speechwriters are now Washington Post columnists); there were “research” positions (after losing his Senate seat, Rick Santorum became director of the “America’s Enemies” program at a think tank supported by the Koch brothers, among others).

The combination of a successful electoral strategy and the safety net made being a conservative loyalist a seemingly low-risk professional path. The cause was radical, but the people it recruited tended increasingly to be apparatchiks, motivated more by careerism than by conviction.

That’s certainly the impression Cantor conveyed. I’ve never heard him described as inspiring. His political rhetoric was nasty but low-energy, and often amazingly tone-deaf. You may recall, for example, that in 2012 he chose to celebrate Labor Day with a Twitter post honoring business owners. But he was evidently very good at playing the inside game.

It turns out, however, that this is no longer enough. We don’t know exactly why he lost his primary, but it seems clear that Republican base voters didn’t trust him to serve their priorities as opposed to those of corporate interests (and they were probably right). And the specific issue that loomed largest, immigration, also happens to be one on which the divergence between the base and the party elite is wide. It’s not just that the elite believes that it must find a way to reach Hispanics, whom the base loathes. There’s also an inherent conflict between the base’s nativism and the corporate desire for abundant, cheap labor.

And while Cantor won’t go hungry — he’ll surely find a comfortable niche on K Street — the humiliation of his fall is a warning that becoming a conservative apparatchik isn’t the safe career choice it once seemed.

So whither movement conservatism? Before the Virginia upset, there was a widespread media narrative to the effect that the Republican establishment was regaining control from the Tea Party, which was really a claim that good old-fashioned movement conservatism was on its way back. In reality, however, establishment figures who won primaries did so only by reinventing themselves as extremists. And Cantor’s defeat shows that lip service to extremism isn’t enough; the base needs to believe that you really mean it.

In the long run — which probably begins in 2016 — this will be bad news for the GOP, because the party is moving right on social issues at a time when the country at large is moving left. (Think about how quickly the ground has shifted on gay marriage.) Meanwhile, however, what we’re looking at is a party that will be even more extreme, even less interested in participating in normal governance, than it has been since 2008. An ugly political scene is about to get even uglier.